1. Field of the Invention
The present invention relates to detecting instruments for use in leak detection of a gas, particularly to a process for manufacturing a reference leak.
2. Discussion of the Related Art
A reference leak is an artificial instrument for use in leak detection of a specific gas. The reference leak has a constant leak rate for the specific gas under a given condition such as a specific temperature and a specific pressure at the gas intake side. The reference leak has been widely used in periodical leak detection and calibration of a helium mass spectrometer leak detector.
Conventional reference leaks can generally be classified into the three types: platinum wire-glass leaks, squeezed metal tube leaks, and silica membrane helium leaks. A leak rate of the platinum wire-glass leak is generally in the range from 10−6˜10−8 torr·l/s. The platinum wire-glass leak is obtained by implanting a platinum wire into a glass body by way of a glass-to-metal unmatched sealing method. Due to a coefficient of thermal expansion of the platinum wire being unmatched with that of the glass body, a plurality of leak gaps are then defined at an interface between the platinum wire and the glass body. The platinum wire-glass leak is then obtained. However, during the manufacturing process of the platinum wire-glass type leak, the leak gaps' shapes, sizes, and numbers are randomly formed and therefore cannot be artificially controlled. A leak rate of the reference leak has to be calibrated by other reference calibration instruments after the reference leak is manufactured. Additionally, the leak rate of the reference leak is sensitive to temperatures. The leak rate may vary due to a change of the number and distribution of the leak gaps as a result of a change of the temperature. This temperature dependence may cause uncertainties (i.e., potential for an increased margin of error) with respect to the leak rate of the platinum wire-glass leak.
The squeezed metal tube leak is generally obtained by punching a tube of an oxygen free copper into a flattened piece by a hydraulic pressure device. The squeezed metal tube comprises a plurality of leak gaps, the leak gaps functioning as leak channels for the gas. A leak rate of the squeezed metal tube type reference leak is generally in the range from 10−6˜10−8 tor·l/s. However, similar to the platinum wire-glass leak, shapes, sizes, and numbers of the leak gaps of the squeezed metal tube leak are also formed randomly making such leak gaps unpredictable and therefore artificially uncontrollable.
The silica membrane helium leak is generally in a form of a blown bubble. The blown bubble is generally a thin, spherical membrane formed of silica glass. The silica glass membrane is porous and allows helium (He) gas to pass therethrough while blocking other kinds of gases from passing therethrough. Likewise, a leak rate of such a reference leak is unpredictable and has to be calibrated by other reference calibration instruments. The leak rate of the reference leak is also sensitive to temperatures.
Therefore, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies with respect to reference leaks and their method of manufacture, in particular.